Photovoltaic cell with thiazole-containing polymer

ABSTRACT

Photovoltaic cells with thiazole-containing polymers, as well as related components, systems, and methods, are disclosed.

This application is a divisional and claims benefit of U.S. applicationSer. No. 13/191,264, filed Jul. 26, 2011, which is a divisional andclaims benefit of U.S. application Ser. No. 11/851,591, filed Sep. 7,2007, now U.S. Pat. No. 8,008,424, which in turn claims benefit of U.S.Provisional Patent Application Ser. No. 60/850,845, filed Oct. 11, 2006.The entire contents of each of the applications are hereby incorporatedby reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

This invention was supported by contract number W911QY-04-C-0070 awardedby the Defense Advanced Research Projects Agency. The U.S. Governmenthas certain rights in the invention.

TECHNICAL FIELD

This invention relates to photovoltaic cells with thiazole-containingpolymers, as well as related components; systems, and methods.

BACKGROUND

Photovoltaic cells are commonly used to transfer energy in the form oflight into energy in the form of electricity. A typical photovoltaiccell includes a photoactive material disposed between two electrodes.Generally, light passes through one or both of the electrodes tointeract with the photoactive material. As a result, the ability of oneor both of the electrodes to transmit light (e.g., light at one or morewavelengths absorbed by a photoactive material) can limit the overallefficiency of a photovoltaic cell. In many photovoltaic cells, a film ofsemiconductive material (e.g., indium tin oxide) is used to form theelectrode(s) through which light passes because, although thesemiconductive material can have a lower electrical conductivity thanelectrically conductive materials, the semiconductive material cantransmit more light than many electrically conductive materials.

SUMMARY

This invention relates to photovoltaic cells with thiazole-containingpolymers (e.g., polymers containing a bithiazole, cyclopentadithiazole,or thiazolothiazole moiety), as well as related components, systems, andmethods.

An aspect of the invention relates to new combinations of monomers forpreparing polymers, which have properties suitable for use as chargecarriers in the active layer of a photovoltaic cell.

In one aspect, this invention features a polymer including a firstcomonomer repeat unit comprising a cyclopentadithiazole moiety; and asecond comonomer repeat unit different from the first comonomer repeatunit.

In another aspect, this invention features a polymer including a firstcomonomer repeat unit comprising a thiazolothiazole moiety; and a secondcomonomer repeat unit different from the first comonomer repeat unit.The second comonomer repeat unit is not a phenyl moiety or a fluorenemoiety.

In another aspect, this invention features a polymer including a firstcomonomer repeat unit comprising a thiazole moiety; and a secondcomonomer repeat unit different from the first comonomer repeat unit.The second comonomer repeat unit is not a thiophene moiety or a fluorenemoiety.

In still another aspect, this invention features an article thatincludes a first electrode, a second electrode, and a photoactivematerial disposed between the first and second electrodes. Thephotoactive material includes a polymer described above. The article isconfigured as a photovoltaic cell.

Embodiments can include one or more of the following features.

In some embodiments, the first comonomer repeat unit includes acyclopentadithiazole moiety of formula (1):

in which each of R₁ and R₂, independently, is H, C₁-C₂₀ alkyl, C₁-C₂₀alkoxy, C₃-C₂₀ cycloalkyl, C₁-C₂₀ heterocycloalkyl, aryl, heteroaryl,halo, CN, OR, C(O)R, C(O)OR, or SO₂R; R being H, C₁-C₂₀ alkyl, C₁-C₂₀alkoxy, aryl, heteroaryl, C₃-C₂₀ cycloalkyl, or C₁-C₂₀ heterocycloalkyl.For example, each of R₁ and R₂, independently, can be C₁-C₂₀ alkoxy orC₁-C₂₀ alkyl optionally substituted with C₁-C₂₀ alkoxy or halo.

In some embodiments, the first comonomer repeat unit comprises athiazole moiety of formula (23):

in which R₅ is H, C₁-C₂₀ alkyl, C₁-C₂₀ alkoxy, C₃-C₂₀ cycloalkyl, C₁-C₂₀heterocycloalkyl, aryl, heteroaryl, halo, CN, OR, C(O)R, C(O)OR, orSO₂R; R being H, C₁-C₂₀ alkyl, C₁-C₂₀ alkoxy, aryl, heteroaryl, C₃-C₂₀cycloalkyl, or C₁-C₂₀ heterocycloalkyl. For example, R₅ can be hexyl.

In some embodiments, the first comonomer repeat unit comprises athiazolothiazole moiety of formula (25):

In some embodiments, the second comonomer repeat unit includes asilacyclopentadithiophene moiety, a benzothiadiazole moiety, athiadiazoloquinoxaline moiety, a cyclopentadithiophene moiety, acyclopentadithiophene oxide moiety, a benzoisothiazole moiety, abenzothiazole moiety, a thiophene oxide moiety, a thienothiophenemoiety, a thienothiophene oxide moiety, a dithienothiophene moiety, adithienothiophene oxide moiety, a tetrahydroisoindole moiety, a fluorenemoiety, a fluorenone moiety, a thiazole moiety, a selenophene moiety, asilole moiety, a thiazolothiazole moiety, a cyclopentadithiazole moiety,a naphthothiadiazole moiety, a thienopyrazine moiety, a thiophenemoiety, an oxazole moiety, an imidazole moiety, a pyrimidine moiety, abenzoxazole moiety, or a benzimidazole moiety.

In some embodiments, the second comonomer repeat unit includes acyclopentadithiazole moiety of formula (1), a benzothiadiazole moiety offormula (2), a thiadiazoloquinoxaline moiety of formula (3), acyclopentadithiophene dioxide moiety of formula (4), acyclopentadithiophene monoxide moiety of formula (5), a benzoisothiazolemoiety of formula (6), a benzothiazole moiety of formula (7), athiophene dioxide moiety of formula (8), a cyclopentadithiophene dioxidemoiety of formula (9), a cyclopentadithiophene tetraoxide moiety offormula (10), a thienothiophene moiety of formula (11), athienothiophene tetraoxide moiety of formula (12), a dithienothiophenemoiety of formula (13), a dithienothiophene dioxide moiety of formula(14), a dithienothiophene tetraoxide moiety of formula (15), atetrahydroisoindole moiety of formula (16), a thienothiophene dioxidemoiety of formula (17), a dithienothiophene dioxide moiety of formula(18), a fluorene moiety of formula (19), a silole moiety of formula(20), a cyclopentadithiophene moiety of formula (21), a fluorenonemoiety of formula (22), a thiazole moiety of formula (23), a selenophenemoiety of formula (24), a thiazolothiazole moiety of formula (25), anaphthothiadiazole moiety of formula (26), a thienopyrazine moiety offormula (27), a silacyclopentadithiophene moiety of formula (28), athiophene moiety of formula (29), an oxazole moiety of formula (30), animidazole moiety of formula (31), a pyrimidine moiety of formula (32), abenzoxazole moiety of formula (33), or a benzimidazole moiety of formula(34):

in which each of X and Y, independently, is CH₂, O, or S; each of R₅ andR₆, independently, is H, C₁-C₂₀ alkyl, C₁-C₂₀ alkoxy, C₃-C₂₀ cycloalkyl,C₁-C₂₀ heterocycloalkyl, aryl, heteroaryl, halo, CN, OR, C(O)R, C(O)OR,or SO₂R, in which R is H, C₁-C₂₀ alkyl, C₁-C₂₀ alkoxy, aryl, heteroaryl,C₃-C₂₀ cycloalkyl, or C₁-C₂₀ heterocycloalkyl; and each of R₇ and R₈,independently, is H, C₁-C₂₀ alkyl, C₁-C₂₀ alkoxy, aryl, heteroaryl,C₃-C₂₀ cycloalkyl, or C₃-C₂₀ heterocycloalkyl.

In some embodiments, the polymer further includes a third comonomerrepeat unit different from the first and second comonomer repeat units.The third comonomer repeat unit can include a thiophene moiety (e.g., aunsubstituted or substituted thiophene moiety).

In some embodiments, the polymer can be either an electron donormaterial or an electron acceptor material.

In some embodiments, the polymer can be

in which n can be an integer greater than 1.

In some embodiments, the photovoltaic cell can be a tandem photovoltaiccell.

In some embodiments, the photoactive material can include an electronacceptor material. In some embodiments, the electron acceptor materialcan be a fullerene (e.g., C61-phenyl-butyric acid methyl ester, PCBM).

In some embodiments, the polymer and the electron acceptor material eachcan have a LUMO energy level. The LUMO energy level of the polymer canbe at least about 0.2 eV (e.g., at least about 0.3 eV) less negativethan the LUMO energy level of the electron acceptor material.

In some embodiments, the device can be an organic semiconductive device.In certain embodiments, the device can be a member selected from thegroup consisting of field effect transistors, photodetectors,photovoltaic detectors, imaging devices, light emitting diodes, lasingdevices, conversion layers, amplifiers and emitters, storage elements,and electrochromic devices.

Embodiments can provide one or more of the following advantages.

In some embodiments, using a polymer containing a thiazole moiety can beadvantageous because the thiazole moiety can contribute to a shift inthe maximum absorption wavelength toward the red or near IR region ofthe electromagnetic spectrum. When such a polymer is incorporated into aphotovoltaic cell, the current and efficiency of the cell can increase.

In some embodiments, substituted fullerenes or polymers containingsubstituted monomer repeat units (e.g., substituted with long-chainalkoxy groups such as oligomeric ethylene oxides or fluorinated alkoxygroups) can have improved solubility in organic solvents and can form aphotoactive layer with improved morphology.

In some embodiments, a polymer containing a thiazole moiety can absorblight at a relatively long wavelength and have improved solubility inorganic solvents. In some embodiments, a polymer containing a thiazolemoiety can be used to prepare an electron donor material with improvedsemiconductive properties.

In some embodiments, a photovoltaic cell containing a polymer describedabove can have a band gap that is relatively ideal for its intendedpurposes.

In some embodiments, a photovoltaic cell having high cell voltage can becreated, whereby the HOMO level of the polymer is at least about 0.2electron volts more negative relative to the LUMO or conduction band ofan electron acceptor material.

In some embodiments, a photovoltaic cell containing a polymer describedabove can have relatively fast and efficient transfer of an electron toan electron acceptor material, whereby the LUMO of the donor is at leastabout 0.2 electron volt (e.g., at least about 0.3 electron volt) lessnegative than the conduction band of the electron acceptor material.

In some embodiments, a photovoltaic cell containing a polymer describedabove can have relatively fast charge separation, whereby the chargemobility of the positive charge, or hole, is relatively high and fallswithin the range of 10⁻⁴ to 10⁻¹ cm²/Vs.

In some embodiments, the polymer is soluble in an organic solvent and/orfilm forming.

In some embodiments, the polymer is optically non-scattering.

In some embodiments, the polymer can be used in organic field effecttransistors and OLEDs.

Other features and advantages of the invention will be apparent from thedescription, drawings, and claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of an embodiment of a photovoltaiccell.

FIG. 2 is a schematic of a system containing one electrode between twophotoactive layers.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

FIG. 1 shows a cross-sectional view of a photovoltaic cell 100 thatincludes a substrate 110, a cathode 120, a hole carrier layer 130, anactive layer 140 (containing an electron acceptor material and anelectron donor material), a hole blocking layer 150, an anode 160, and asubstrate 170.

In general, during use, light impinges on the surface of substrate 110,and passes through substrate 110, cathode 120, and hole carrier layer130. The light then interacts with active layer 140, causing electronsto be transferred from the electron donor material (e.g., a polymerdescribed above) to the electron acceptor material (e.g., PCBM). Theelectron acceptor material then transmits the electrons through holeblocking layer 150 to anode 160, and the electron donor materialtransfers holes through hole carrier layer 130 to cathode 120. Anode 160and cathode 120 are in electrical connection via an external load sothat electrons pass from anode 160, through the load, and to cathode120.

Electron acceptor materials of active layer 140 can include fullerenes.In some embodiments, active layer 140 can include one or moreunsubstituted fullerenes and/or one or more substituted fullerenes.Examples of unsubstituted fullerenes include C₆₀, C₇₀, C₇₆, C₇₈, C₈₂,C₈₄, and C₉₂. Examples of substituted fullerenes include PCBM orfullerenes substituted with C₁-C₂₀ alkoxy optionally further substitutedwith C₁-C₂₀ alkoxy or halo (e.g., (OCH₂CH₂)₂OCH₃ or OCH₂CF₂OCF₂CF₂OCF₃).Without wishing to be bound by theory, it is believed that fullerenessubstituted with long-chain alkoxy groups (e.g., oligomeric ethyleneoxides) or fluorinated alkoxy groups have improved solubility in organicsolvents and can form a photoactive layer with improved morphology.

In some embodiments, the electron acceptor materials can includepolymers (e.g., homopolymers or copolymers). A polymers mentioned hereininclude at least two identical or different monomer repeat units (e.g.,at least 5 monomer repeat units, at least 10 monomer repeat units, atleast 50 monomer repeat units, at least 100 monomer repeat units, or atleast 500 monomer repeat units). A copolymer mentioned herein refers toa polymer that includes at least two co-monomers of differingstructures. In some embodiments, the polymers used as an electronacceptor material can include one or more monomer repeat units listed inTables 1 and 2 below. Specifically, Table 1 lists examples of electrondonating monomer repeat units that can serve as a conjugative link.Table 2 lists examples of electron withdrawing monomer repeat units.Note that depending on the substituents, monomer repeat units listed inTable 1 can be electron withdrawing and monomer repeat units listed inTable 2 can also be electron donating. Preferably, the polymers used asan electron acceptor material include a high molar percentage (e.g., atleast about 50%, at least about 60%, at least about 70%, at least about80%, at least about 90%) of an electron withdrawing monomer repeat unit.

Electron donor materials of active layer 140 can include polymers (e.g.,homopolymers or copolymers). In some embodiments, the polymers used asan electron donor material can include one or more monomer repeat unitslisted in Tables 1 and 2. Preferably, the polymers used as an electrondonor material include a high molar percentage (e.g., at least about50%, at least about 60%, at least about 70%, at least about 80%, atleast about 90%) of an electron donating monomer repeat unit. In someembodiments, the polymers include a monomer repeat unit containingC₁-C₂₀ alkoxy on a ring, which is optionally further substituted withC₁-C₂₀ alkoxy or halo (e.g., (OCH₂CH₂)₂OCH₃ or OCH₂CF₂OCF₂CF₂OCF₃).Without wishing to be bound by theory, it is believed that polymerscontaining monomer repeat units substituted with long-chain alkoxygroups (e.g., oligomeric ethylene oxides) or fluorinated alkoxy groupshave improved solubility in organic solvents and can form an photoactivelayer with improved morphology.

TABLE 1

TABLE 2

Referring to formulas listed in Tables 1 and 2 above, each of X and Y,independently, can be CH₂, O, or S; each of R₁, R₂, R₅, and R₆,independently, can be H, C₁-C₂₀ alkyl (e.g., branched alkyl orperflorinated alkyl), C₁-C₂₀ alkoxy, C₃-C₂₀ cycloalkyl, C₁-C₂₀heterocycloalkyl, aryl (e.g., phenyl or substituted phenyl), heteroaryl,halo, CN, OR, C(O)R, C(O)OR, or SO₂R; R being H, C₁-C₂₀ alkyl, C₁-C₂₀alkoxy, aryl, heteroaryl, C₃-C₂₀ cycloalkyl, or C₁-C₂₀ heterocycloalkyl;and each of R₇ and R₈, independently, is H, C₁-C₂₀ alkyl, C₁-C₂₀ alkoxy,aryl, heteroaryl, C₃-C₂₀ cycloalkyl, or C₃-C₂₀ heterocycloalkyl.

An alkyl can be saturated or unsaturated and branch or straight chained.A C₁-C₂₀ alkyl contains 1 to 20 carbon atoms (e.g., one, two, three,four, five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15, 16, 17, 18,19, and 20 carbon atoms). Examples of alkyl moieties include —CH₃,—CH₂—, —CH₂═CH₂—, —CH₂—CH═CH₂, and branched —C₃H₇. An alkoxy can bebranch or straight chained and saturated or unsaturated. A C₁-C₂₀ alkoxycontains an oxygen radical and 1 to 20 carbon atoms (e.g., one, two,three, four, five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15, 16,17, 18, 19, and 20 carbon atoms). Examples of alkoxy moieties include—OCH₃ and —OCH═CH—CH₃. A cycloalkyl can be either saturated orunsaturated. A C₃-C₂₀ cycloalkyl contains 3 to 20 carbon atoms (e.g.,three, four, five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15, 16,17, 18, 19, and 20 carbon atoms). Examples of cycloalkyl moieitiesinclude cyclohexyl and cyclohexen-3-yl. A heterocycloalkyl can also beeither saturated or unsaturated. A C₃-C₂₀ heterocycloalkyl contains atleast one ring heteroatom (e.g., O, N, and S) and 3 to 20 carbon atoms(e.g., three, four, five, six, seven, eight, nine, 10, 11, 12, 13, 14,15, 16, 17, 18, 19, and 20 carbon atoms). Examples of heterocycloalkylmoieties include 4-tetrahydropyranyl and 4-pyranyl. An aryl can containone or more aromatic rings. Examples of aryl moieties include phenyl,phenylene, naphthyl, naphthylene, pyrenyl, anthryl, and phenanthryl. Aheteroaryl can contain one or more aromatic rings, at least one of whichcontains at least one ring heteroatom (e.g., O, N, and S). Examples ofheteroaryl moieties include furyl, furylene, fluorenyl, pyrrolyl,thienyl, oxazolyl, imidazolyl, thiazolyl, pyridyl, pyrimidinyl,quinazolinyl, quinolyl, isoquinolyl, and indolyl.

Alkyl, alkoxy, cycloalkyl, heterocycloalkyl, aryl, and heteroarylmentioned herein include both substituted and unsubstituted moieties,unless specified otherwise. Examples of substituents on cycloalkyl,heterocycloalkyl, aryl, and heteroaryl include C₁-C₂₀ alkyl, C₃-C₂₀cycloalkyl, C₁-C₂₀ alkoxy, aryl, aryloxy, heteroaryl, heteroaryloxy,amino, C₁-C₁₀ alkylamino, C₁-C₂₀ dialkylamino, arylamino, diarylamino,hydroxyl, halogen, thio, C₁-C₁₀ alkylthio, arylthio, C₁-C₁₀alkylsulfonyl, arylsulfonyl, cyano, nitro, acyl, acyloxy, carboxyl, andcarboxylic ester. Examples of substituents on alkyl include all of theabove-recited substituents except C₁-C₂₀ alkyl. Cycloalkyl,heterocycloalkyl, aryl, and heteroaryl also include fused groups.

The monomers for preparing the polymers mentioned herein may contain anon-aromatic double bond and one or more asymmetric centers. Thus, theycan occur as racemates and racemic mixtures, single enantiomers,individual diastereomers, diastereomeric mixtures, and cis- ortrans-isomeric forms. All such isomeric forms are contemplated.

The copolymers described above can be prepared by methods known in theart. For example, a copolymer can be prepared by a cross-couplingreaction between one or more comonomers containing two alkylstannylgroups and one or more comonomers containing two halo groups in thepresence of a transition metal catalyst. As another example, a copolymercan be prepared by a cross-coupling reaction between one or morecomonomers containing two borate groups and one or more comonomerscontaining two halo groups in the presence of a transition metalcatalyst. The comonomers can be prepared by the methods described hereinor by the methods know in the art, such as those described in U.S.patent application Ser. No. 11/486,536, Coppo et al., Macromolecules2003, 36, 2705-2711 and Kurt et al., J. Heterocycl. Chem. 1970, 6, 629,the contents of which are hereby incorporated by reference.

The monomers for preparing the copolymers described above are eithercommercially available or can be prepared by methods known in the art.For example, a cyclopentadithiazole monomer can be prepared by themethod illustrated in Scheme I below. The cyclopentadithiazole monomerthus obtained can then react with another monomer (such as those shownin Scheme II below) to form a copolymer described above.

Table 3 below lists an exemplary polymer (i.e., polymer 1) described inthe Summary section above. This polymer can have unique properties,which make it particularly suitable as a charge carrier in the activelayer of a photovoltaic cell. For example, an organic photovoltaic cellinclude this polymer in the active layer can have an efficiency morethan 3%. Polymer 1 can be obtained by the methods described in Example 2below.

Generally, one co-monomer in the polymers described in the Summarysection above contains a thiazole moiety (e.g., a bithiazole,thiazolothiazole, or cyclopentadithiazole moiety). An advantage of aco-polymer containing a thiazole moiety is that its absorptionwavelength can shift toward the red and near IR portion (e.g., 650-800nm) of the electromagnetic spectrum, which is not accessible by mostother polymers. When such a co-polymer is incorporated into aphotovoltaic cell, it enables the cell to absorb the light in thisregion of the spectrum, thereby increasing the current and efficiency ofthe cell.

The polymers described above can be useful in solar power technologybecause the band gap is close to ideal for a photovoltaic cell (e.g., apolymer-fullerene cell). The HOMO level of the polymers can bepositioned correctly relative to the LUMO of an electron acceptor (e.g.,PCBM) in a photovoltaic cell (e.g., a polymer-fullerene cell), allowingfor high cell voltage. The LUMO of the polymers can be positionedcorrectly relative to the conduction band of the electron acceptor in aphotovoltaic cell, thereby creating efficient transfer of an electron tothe electron acceptor. For example, using a polymer having a band gap ofabout 1.4-1.6 eV can significantly enhance cell voltage. Cellperformance, specifically efficiency, can benefit from both an increasein photocurrent and an increase in cell voltage, and can approach andeven exceed 15% efficiency. The positive charge mobility of the polymerscan be relatively high and approximately in the range of 10⁻⁴ to 10⁻¹cm²/Vs. In general, the relatively high positive charge mobility allowsfor relatively fast charge separation. The polymers can also be solublein an organic solvent and/or film forming. Further, the polymers can beoptically non-scattering.

Components in photovoltaic cell other than the electron acceptormaterials and the electron donor materials are known in the art, such asthose described in U.S. patent application Ser. No. 10/723,554, thecontents of which are incorporated herein by references.

In some embodiments, the polymer described above can be used as anelectron donor material or an electro acceptor material in a system inwhich two photovoltaic cells share a common electrode. Such a system isalso known as tandem photovoltaic cell. Examples of tandem photovoltaiccells are discussed in U.S. patent application Ser. No. 10/558,878,filed Nov. 29, 2005, the contents of which are hereby incorporated byreference.

As an example, FIG. 2 is a schematic of a tandem photovoltaic cell 200having a substrate 210, three electrodes 220, 240, and 260, and twophotoactive layers 230 and 250. Electrode 240 is shared betweenphotoactive layers 230 and 250, and is electrically connected withelectrodes 220 and 260. In general, electrodes 220, 240, and 260 can beformed of an electrically conductive material, such as those describedin U.S. patent application Ser. No. 10/723,554. In some embodiments, oneor more (i.e., one, two, or three) electrodes 220, 240, and 260 is amesh electrode. In some embodiments, one or more electrodes 220, 240,and 260 is formed of a semiconductive material. Examples ofsemiconductive materials include titanium oxides, indium tin oxides,fluorinated tin oxides, tin oxides, and zinc oxides. In certainembodiments, one or more (i.e., one, two, or three) electrodes 220, 240,and 260 are formed of titanium dioxide. Titanium dioxide used to preparean electrode can be in any suitable forms. For example, titanium dioxidecan be in the form of interconnected nanoparticles. Examples ofinterconnected titanium dioxide nanoparticles are described, forexample, in U.S. Pat. No. 7,022,910, the contents of which areincorporated herein by reference. In some embodiments, at least one(e.g., one, two, or three) of electrodes 220, 240, and 260 is atransparent electrode. As referred to herein, a transparent electrode isformed of a material which, at the thickness used in a photovoltaiccell, transmits at least about 60% (e.g., at least about 70%, at leastabout 75%, at least about 80%, at least about 85%, at least about 90%,at least about 95%) of incident light at a wavelength or a range ofwavelengths used during operation of the photovoltaic cell. In certainembodiments, both electrodes 220 and 260 are transparent electrodes.

Each of photoactive layers 230 and 250 can contain at least onesemiconductive material. In some embodiments, the semiconductivematerial in photoactive layer 230 has the same band gap as thesemiconductive material in photoactive layer 250. In certainembodiments, the semiconductive material in photoactive layer 230 has aband gap different from that of the semiconductive material inphotoactive layer 250. Without wishing to be bound by theory, it isbelieved that incident light not absorbed by one photoactive layer canbe absorbed by the other photoactive layer, thereby maximizing theabsorption of the incident light.

In some embodiments, at least one of photoactive layers 230 and 250 cancontain an electron acceptor material (e.g., PCBM or a polymer describedabove) and an electron donor material (e.g., a polymer described above).In general, suitable electron acceptor materials and electron donormaterials can be those described above. In certain embodiments, each ofphotoactive layers 230 and 250 contains an electron acceptor materialand an electron donor material.

Substrate 210 can be formed of one or more suitable polymers, such asthose described in U.S. patent application Ser. No. 10/723,554. In someembodiments, an additional substrate (not shown in FIG. 2) can bedisposed on electrode 260.

Photovoltaic cell 200 can further contain a hole carrier layer (notshown in FIG. 2) and a hole blocking layer (not shown in FIG. 2), suchas those described in U.S. patent application Ser. No. 10/723,554.

While photovoltaic cells have been described above, in some embodiments,the polymers described herein can be used in other devices and systems.For example, the polymers can be used in suitable organic semiconductivedevices, such as field effect transistors, photodetectors (e.g., IRdetectors), photovoltaic detectors, imaging devices (e.g., RGB imagingdevices for cameras or medical imaging systems), light emitting diodes(LEDs) (e.g., organic LEDs or IR or near IR LEDs), lasing devices,conversion layers (e.g., layers that convert visible emission into IRemission), amplifiers and emitters for telecommunication (e.g., dopantsfor fibers), storage elements (e.g., holographic storage elements), andelectrochromic devices (e.g., electrochromic displays).

The following examples are illustrative and not intended to be limiting.

EXAMPLE 1 Preparation of2,6-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-4H-4,4-bis(2′-ethylhexyl)cyclopenta[2,1-b:3,4-b′]thiophene

100 mL oven dried Schlenk flask was charged with 1.097 g (2.72 mmol) of4H-4,4-bis(2′-ethylhexyl)cyclopenta[2,1-b:3,4-b′]dithiophene. The flaskwas evacuated and purged with argon three times. To this flask was thenadded 20 mL of dry, distilled THF. The resulting solution was cooled to−78° C. and 4.35 mL (10.88 mmol, 4 equv.) of 2.5M BuLi was addeddropwise. The reaction was stirred for 1 hout at −78° C. and then warmedto room temperature and stirred for an additional 3 hours. The solutionwas cooled again to −78° C. and 2.77 mL (13.6 mmol, 5 equiv.) of2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane was added in oneportion via syringe. The reaction was stirred at −78° C. for 1 hour andthen allowed to warm to room temperature overnight. The solution waspoured into water and extracted with 4×150 mL of methyl tert-butylether. The organic layers were combined and washed with 2×150 mL ofbrine, dried with anhydrous MgSO₄, and filtered. The solvent was removedunder vacuum to yield and orange oil, which was purified by columnchromatography (5% EtOAc in hexanes) to yield a colorless, viscous oil,1.34 g (75% yield).

EXAMPLE 2 Preparation of Polymer 1

A 100 mL Schlenk flask was charged with 0.1515 g (0.231 mmol) of2,6-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-4H-4,4-bis(2′-ethylhexyl)cyclopenta[2,1-b:3,4-b′]thiophene,0.152 g (0.231 mmol) of5,5′-bis(5-bromo-2-thienyl)-4,4′-dihexyl-2,2′-bithiazole, 2.1 mg Pd₂dba₃ (0.00231 mmol), 4.2 mg PPh₃ (0.0162 mmol), and 35 mg (0.0855 mmol)of Aliquat 336. The flask, which was fitted with a condenser, was thenevacuated and refilled with argon three times. The reagents weredissolved in a mixture of 20 mL of THF and 15 mL of toluene. 2 mL of a2M Na₂CO₃ aquesous solution was added to the above solution whilestirring. The reaction was heated at 90° C. for 3 days. A 1 mL THFsolution of 14 mg (0.1155 mmol) of phenylboronic acid and 1.6 mg(0.00231 mmol) of PdCl₂(PPh₃)₂ was added. Heating was continued for anadditional 24 hours. After the reaction was then cooled to 80° C., 10 mLof a 7.5% sodium diethyldithiocarbamate solution in water was added. Themixture was heated at 80° C. with stirring for 18 hours. After thereaction was cooled, the organic layer was separated and washed withwarm water (3×100 mL). The toluene solution was concentrated and thenpoured into 750 mL of stirring MeOH. After the solution was filtered,the dark precipitate was collected and washed with MeOH. The precipitatewas then transferred to a Soxhlet thimble and washed with acetoneovernight. The product thus obtained was dried under vacuum to give0.176 g of brown solid (0.195 mmol, 84%). ¹H NMR (200 MHz, CDCl₃): δ7.2-7.1 (br, 6H), 3.0 (m, 4H), 1.86 (m, 8H), 1.6 (br, 16H), 1.20-0.65(br, 32H).

Other embodiments are in the claims.

What is claimed is:
 1. An article, comprising: a first electrode; asecond electrode; and a photoactive material disposed between the firstand second electrodes, the photoactive material comprising a polymerincluding a first comonomer repeat unit and a second comonomer repeatunit different from the first comonomer repeat unit; wherein the firstcomonomer repeat unit comprises a thiazole moiety; the second comonomerrepeat unit is not a thiophene moiety or a fluorene moiety; and thearticle is configured as a photovoltaic cell.
 2. The article of claim 1,wherein the first comonomer repeat unit comprises a thiazole moiety offormula (23):

wherein R₅ is H, C₁-C₂₀ alkyl, C₁-C₂₀ alkoxy, C₃-C₂₀ cycloalkyl, C₁-C₂₀heterocycloalkyl, aryl, heteroaryl, halo, CN, OR, C(O)R, C(O)OR, orSO₂R; R being H, C₁-C₂₀ alkyl, C₁-C₂₀ alkoxy, aryl, heteroaryl, C₃-C₂₀cycloalkyl, or C₁-C₂₀ heterocycloalkyl.
 3. The article of claim 2,wherein R₅ is C₁-C₂₀ alkoxy or C₁-C₂₀ alkyl optionally substituted withC₁-C₂₀ alkoxy or halo.
 4. The article of claim 3, wherein R₅ is hexyl.5. The article of claim 1, wherein the second comonomer repeat unitcomprises a silacyclopentadithiophene moiety, a benzothiadiazole moiety,a thiadiazoloquinoxaline moiety, a cyclopentadithiophene moiety, acyclopentadithiophene oxide moiety, a benzoisothiazole moiety, abenzothiazole moiety, a thiophene oxide moiety, a thienothiophenemoiety, a thienothiophene oxide moiety, a dithienothiophene moiety, adithienothiophene oxide moiety, a tetrahydroisoindole moiety, afluorenone moiety, a thiazole moiety, a selenophene moiety, a silolemoiety, a thiazolothiazole moiety, a cyclopentadithiazole moiety, anaphthothiadiazole moiety, a thienopyrazine moiety, an oxazole moiety,an imidazole moiety, a pyrimidine moiety, a benzoxazole moiety, or abenzimidazole moiety.
 6. The article of claim 5, wherein the secondcomonomer repeat unit comprises a cyclopentadithiazole moiety of formula(1), a benzothiadiazole moiety of formula (2), a thiadiazoloquinoxalinemoiety of formula (3), a cyclopentadithiophene dioxide moiety of formula(4), a cyclopentadithiophene monoxide moiety of formula (5), abenzoisothiazole moiety of formula (6), a benzothiazole moiety offormula (7), a thiophene dioxide moiety of formula (8), acyclopentadithiophene dioxide moiety of formula (9), acyclopentadithiophene tetraoxide moiety of formula (10), athienothiophene moiety of formula (11), a thienothiophene tetraoxidemoiety of formula (12), a dithienothiophene moiety of formula (13), adithienothiophene dioxide moiety of formula (14), a dithienothiophenetetraoxide moiety of formula (15), a tetrahydroisoindole moiety offormula (16), a thienothiophene dioxide moiety of formula (17), adithienothiophene dioxide moiety of formula (18), a silole moiety offormula (20), a cyclopentadithiophene moiety of formula (21), afluorenone moiety of formula (22), a thiazole moiety of formula (23), aselenophene moiety of formula (24), a thiazolothiazole moiety of formula(25), a naphthothiadiazole moiety of formula (26), a thienopyrazinemoiety of formula (27), a silacyclopentadithiophene moiety of formula(28), an oxazole moiety of formula (30), an imidazole moiety of formula(31), a pyrimidine moiety of formula (32), a benzoxazole moiety offormula (33), or a benzimidazole moiety of formula (34):

wherein each of X and Y, independently, is CH₂, O, or S; each of R₁, R₂,R₅ and R₆, independently, is H, C₁-C₂₀ alkyl, C₁-C₂₀ alkoxy, C₃-C₂₀cycloalkyl, C₁-C₂₀ heterocycloalkyl, aryl, heteroaryl, halo, CN, OR,C(O)R, C(O)OR, or SO₂R, in which R is H, C₁-C₂₀ alkyl, C₁-C₂₀ alkoxy,aryl, heteroaryl, C₃-C₂₀ cycloalkyl, or C₁-C₂₀ heterocycloalkyl; andeach of R₇ and R₈, independently, is H, C₁-C₂₀ alkyl, C₁-C₂₀ alkoxy,aryl, heteroaryl, C₃-C₂₀ cycloalkyl, or C₃-C₂₀ heterocycloalkyl.
 7. Thearticle of claim 6, wherein the second comonomer repeat unit comprisesthe cyclopentadithiazole moiety of formula (1), thecyclopentadithiophene moiety of formula (21), or thesilacyclopentadithiophene moiety of formula (28).
 8. The article ofclaim 1, further comprising a third comomoner repeat unit different fromthe first and second comonomer repeat units.
 9. The article of claim 8,wherein the third comomoner repeat unit comprises a thiophene moiety.10. A polymer, comprising: a first comonomer repeat unit comprising athiazole moiety; and a second comonomer repeat unit different from thefirst comonomer repeat unit, the second comonomer repeat unit not beinga thiophene moiety or a fluorene moiety.
 11. The polymer of claim 10,wherein the first comonomer repeat unit comprises a thiazole moiety offormula (23):

wherein R₅ is H, C₁-C₂₀ alkyl, C₁-C₂₀ alkoxy, C₃-C₂₀ cycloalkyl, C₁-C₂₀heterocycloalkyl, aryl, heteroaryl, halo, CN, OR, C(O)R, C(O)OR, orSO₂R; R being H, C₁-C₂₀ alkyl, C₁-C₂₀ alkoxy, aryl, heteroaryl, C₃-C₂₀cycloalkyl, or C₁-C₂₀ heterocycloalkyl.
 12. The polymer of claim 11,wherein R₅ is C₁-C₂₀ alkoxy or C₁-C₂₀ alkyl optionally substituted withC₁-C₂₀ alkoxy or halo.
 13. The polymer of claim 12, wherein R₅ is hexyl.14. The polymer of claim 10, wherein the second comonomer repeat unitcomprises a silacyclopentadithiophene moiety, a benzothiadiazole moiety,a thiadiazoloquinoxaline moiety, a cyclopentadithiophene moiety, acyclopentadithiophene oxide moiety, a benzoisothiazole moiety, abenzothiazole moiety, a thiophene oxide moiety, a thienothiophenemoiety, a thienothiophene oxide moiety, a dithienothiophene moiety, adithienothiophene oxide moiety, a tetrahydroisoindole moiety, afluorenone moiety, a thiazole moiety, a selenophene moiety, a silolemoiety, a thiazolothiazole moiety, a cyclopentadithiazole moiety, anaphthothiadiazole moiety, a thienopyrazine moiety, an oxazole moiety,an imidazole moiety, a pyrimidine moiety, a benzoxazole moiety, or abenzimidazole moiety.
 15. The polymer of claim 14, wherein the secondcomonomer repeat unit comprises a cyclopentadithiazole moiety of formula(1), a benzothiadiazole moiety of formula (2), a thiadiazoloquinoxalinemoiety of formula (3), a cyclopentadithiophene dioxide moiety of formula(4), a cyclopentadithiophene monoxide moiety of formula (5), abenzoisothiazole moiety of formula (6), a benzothiazole moiety offormula (7), a thiophene dioxide moiety of formula (8), acyclopentadithiophene dioxide moiety of formula (9), acyclopentadithiophene tetraoxide moiety of formula (10), athienothiophene moiety of formula (11), a thienothiophene tetraoxidemoiety of formula (12), a dithienothiophene moiety of formula (13), adithienothiophene dioxide moiety of formula (14), a dithienothiophenetetraoxide moiety of formula (15), a tetrahydroisoindole moiety offormula (16), a thienothiophene dioxide moiety of formula (17), adithienothiophene dioxide moiety of formula (18), a silole moiety offormula (20), a cyclopentadithiophene moiety of formula (21), afluorenone moiety of formula (22), a thiazole moiety of formula (23), aselenophene moiety of formula (24), a thiazolothiazole moiety of formula(25), a naphthothiadiazole moiety of formula (26), a thienopyrazinemoiety of formula (27), a silacyclopentadithiophene moiety of formula(28), an oxazole moiety of formula (30), an imidazole moiety of formula(31), a pyrimidine moiety of formula (32), a benzoxazole moiety offormula (33), or a benzimidazole moiety of formula (34):

wherein each of X and Y, independently, is CH₂, O, or S; each of R₁, R₂,R₅ and R₆, independently, is H, C₁-C₂₀ alkyl, C₁-C₂₀ alkoxy, C₃-C₂₀cycloalkyl, C₁-C₂₀ heterocycloalkyl, aryl, heteroaryl, halo, CN, OR,C(O)R, C(O)OR, or SO₂R, in which R is H, C₁-C₂₀ alkyl, C₁-C₂₀ alkoxy,aryl, heteroaryl, C₃-C₂₀ cycloalkyl, or C₁-C₂₀ heterocycloalkyl; andeach of R₇ and R₈, independently, is H, C₁-C₂₀ alkyl, C₁-C₂₀ alkoxy,aryl, heteroaryl, C₃-C₂₀ cycloalkyl, or C₃-C₂₀ heterocycloalkyl.
 16. Thepolymer of claim 15, wherein the second comonomer repeat unit comprisesthe cyclopentadithiazole moiety of formula (1), thecyclopentadithiophene moiety of formula (21), or thesilacyclopentadithiophene moiety of formula (28).
 17. The polymer ofclaim 10, further comprising a third comomoner repeat unit differentfrom the first and second comonomer repeat units.
 18. The polymer ofclaim 17, wherein the third comomoner repeat unit comprises a thiophenemoiety.